"This is a very important photo because it shows mating occurring between 2 different species of Phyllidiella โ Phyllidiella rudmani (on top) and Phyllidiella lizae (below). This demonstrates cross-species mating does sometimes occur in phyllidiid nudibranchs. It has also been demonstrated in Chromodorididae (Risbecia spp.) and in Aglajidae bubble snails (Chelidonura spp.)."